Variable displacement pump control



April 20, 1965 'r. auozaba-l 3,179,061

VARIABLE DISPLACEMENT PUMP CONTROL film men. 23. 1962 4 Sheets-Sheet 1INVENTOR. 74 05052 BuDZ/CH 4 ITOIP/VWS April 20, 1965 1-. BUDZICHVARIABLE DISPLACEMENT PUMP CONTROL 4 Sheets Sheet 2 Filed Feb. 23. 1962INVENTOR. 7A0U5Z 300 21c H April 1965 "r. BUDZICH 3,1 $9,061

VARIABLE DISPLACEMENT PUMP commm Filed Feb. 23. 1962 4 Sheets-Sheet aINVENTOR. 740F052 BUDZ/CH April 20, 1965 Filed Feb. 23. 1962 T. BUDZICH3,179,061

VARIABLE DISPLACEMENT PUMP ,COfiTROL 4 Sheets-Sheet 4 INVEN TOR. 7405052 5002/01 BY E/(HEX MS'NE'N/V Y: FA me lms ro/v A770 A/EYS UnitedStates Patent 3 179 061 VARIABLE DISPLACEMENT PUMP CONTROL TadeuszBudzich, Shaker Heights, Ohio, assignor to The vvfegglierhead Company,Cleveland, Ohio, a corporation 0 o Filed Feb. 23, 1962, Ser. No. 175,201Claims. (Cl. 103-173) This invention relates generally to hydraulicpumps and more particularly to controls for regulating the displacementof variable positive displacement pumps.

It is a primary object of this invention to provide a variabledisplacement pump having a displacement controlling member which ismovable by a fluid motor controlled by a valve which can be operatedremotely by manual movement, in which movement of the valving memberrequires a force which is variable in proportion to the position of thedisplacement controlling member to give the operator a feel for thecontrolled position.

It is another object of this invention to provide a variabledisplacement pump having a displacement controlling member movable by afluid motoroperated through a manual control valve by the outlet fluidpressure, in which the operation of the control is independent ofvariation in the outlet pressure level. i

It is another object of this invention to provide a variabledisplacement pump having a control va ve for a fluid motor for shiftinga displacement controlling member in which the control valve is operablewith a minimum of applied force through a minimum distance of movementfor rapid response under manual control.

It is still another object of this invention to provide a control valvefor a fluid motor for shifting the displacement controlling member in avariable displacement pump, in which the control valve includes a valvespool whose motion and position is controlled by opposing variableforces including a variable spring bias tending to shift the valve spoolin one direction and applied through remote control by the operator andan opposing or counterbalancing force proportional tothe controlpressure in the fluid motor actuating thedisplacement controlling memberand in which the control pressure is variable in proportion to theposition of this displacement controlling member. i

. The invention is shown as applied to a modified pump of the typedisclosed in this inventors co-pending applications, Serial No. 825,005,filed July 6, 1959, now Patent No. 3,090,312 reissued as Patent No.25,553 and Serial No. 88,142, filed February 9, 1961, now Patent No.3,087,- 432. The pump includes a hollow pump housing containing acylinder block mounted for axially sliding movement within the housing.The cylinder block contains a plurality of axially extending cylinderbores, each containing a piston which is reciprocated through a Wobbleplate drive assembly. Inlet ports are formed in the cylinder blockopening into the cylinder bores intermediate the ends, and the ends ofthe cylinder bores opposite the pumping pistons contain floatingreaction pistons which make sealing contact with check valve assembliesin an end housing which collects the outletfluid. The effective outputdisplacement of the pump depends upon the position of the inlet portrelative to the pumping piston stroke since the point at which thepiston blocks off the inlet port determines the start of the effectivepumping stroke of the piston. Thus the axial sliding movement of thecylinder block is employed to vary the effective output displacement ofthe pump between zero and maximum volume.

The control for the shifting of the cylinder block in cludes a fluidpressure motor located axially within the cylinder block assembly andconnected to the control valve mounted on the outside of the pumphousing. The control valve includes a valve spool and ports connected tothe outlet pressure from the pump and drain as well as to the controlpressure in the fluid motor for shifting the cylinder block. Theposition of the valve spool is determined by balancing forces consistingof a variable spring bias applied by an external control tending toshift the spool in one direction. This force is counter-balanced by thecontrol pressure acting on the other end of the pilot valve spool andopposing the adjustable spring bias. The cylinder block is biased to themaximum displacement position by means of a compression spring, andsince the force of this spring will increase as the cylinder block isshifted toward the minimum displacement posi tion, the control pressurewtihin the fluid motor is there- 'fore proportional to the force of thecylinder block spring, since all pumping forces are absorbed on thereaction pistons and do not affect the cylinder block. Therefore, sincethe control pressure will increase as the cylinder block moves towardthe minimum displacement position, the counter-balancing controlpressure force on the pilot valve spool varies in proportion to thecylinder block position, and an increasing force must be applied byincreasing compression of the spring bias on the pilot valve spool andorder to decrease the displacement of the pump.

Further features and advantages of this invention will EQadflyappeartothose skilled in the art upon a more complete understanding of thepreferred embodiment of the invention as shown in the accompanyingdrawings and described in the following detailed description.

In the drawings:

FIG. 1 is a longitudinal cross-sectional view through a pumpincorporating the present invention;

FIG. 2 is an endelevational view of the pump;

FIG. 3 is an enlarged fragmentary cross-sectional view taken along line3-3 of FIG. 2 and showing details of the control valve;

-FIG. 4 is an enlarged fragmentary cross-sectional view taken on line4-4 of FIG. 2;

FIG. 5 is an enlarged fragmentary detail view taken along line 5-5 ofFIG. 2 showing the external connection for the control valve; and

FIG. 6 is an enlarged fragmentary cross-sectional view taken along line6-6 of FIG. 2 and showing details of the pressure compensated valve.

Referring now to FIG. 1 in greater detail, the pump includes a pumphousing 10 defining a fluid chamber 11 therein. The pump housing 10 isformed with an interna cylindrical end portion 12 within which is fittedan outlet housing 13. Outlet housing 13 abuts against an internal flange14 on the pump housing 10 and is held in place by means of set screws 15(see FIG. 4). An -0-ring seal 16 is provided around the'periphery ofoutlet housing 13 to prevent leakage at this point. The pump housing 10is provided with an inlet opening 18 on its side wall for connection toa fluid reservoir to insure that the pump chamber 11 is 'filled withfluid at all times.

The other end of pump housing 19 is-closed ofi" by means of a drivehousing 21) secured to the pump housing by fastening means such as capscrews (not shown). Drive housing 20 is provided with an axial bore 21there through and supports a bearing member 24. A drive member 25 isjournaled by the bearing member 24 and has axially extending shank 26extending outward through bore 21 to engage an oil seal 27 carried bythe drive housing to prevent leakage of fluid out of the housing. Thedrive member 25 is rotatably driven through'a drive shaft 29 which fitswithin a bore 3% in the drive member 25 to make a driving connectionthrough the splined connection indicated at 31. It is understood thatthe drive shaft 29 is rotatably driven by a suitable prime mover foroperating the pump.

On its inner end, drive member 25 is provided with an inclined face 33and a hub portion 34 projecting normal to the inclined face 33. Abearing member 36 is mounted on the inclined-face 33 and hub 34 torotatably journal the wobble plate 38. To prevent the wobble plate 38from rotating with respect to the pump housing 11) a stud 39 projectsradially from the outer periphery of wobble plate 38, and at its outerend, rotatably journals a bearing block 40 which is fitted within alongitudinal guide channel 41 secured within the pump housing. Thus, thewobble plate 38 will not rotate with drive member 25, but will oscillatewith a sinusoidal motion as the drive member 2 is rotated by the driveshaft 2%.

A web member 44 is mounted transversely within the interior of pumphousing 10 a spaced distance from the wobble plate 38. Web member 44 isfixedly .secured in place by means of a pair of snap ring 45 and 46 andserves as a support for various portions of the pump as will bedescribed in greater detail hereinafter.

A cylinder block 51) is slidably journaled Within the end portion 12intermediate the outlet housing 13 and web member 44. Cylinder block 50is mounted for free axial sliding movement between the outlet housing 13and the web member 44 is prevented from rotating within the pump housingby a set or guide screw 51 (see FIG. 4) mounted on the pump housingwall. Set screw 51 has 'a tip portion. 53 which extends into alongitudinal guide slot 52 formed along the outer periphery of cylinderblock 5t) to positively prevent rotation of the cylinder blockregardless of its longitudinal position. 7

The cylinder block 5% is provided with a plurality 0 cylinder bores 55spaced equidistantly around the central axis and extending from end toend through the cylinder block. Since each of the cylinder bores and itsassociated V pumping mechanism is the same, only one cylinder bore hasbeen shown in the drawings and described in greater detail hereinafter.To admit fluid from chamber 11 into the cylinder bores, theeylinderblockstlf has an outer fill- 7 ing slot or port 57 formed on the outerperiphery of the cylinder block intermediate its ends and opening intothe cylinder bore 55 on the outer side. An inner filling slot or port 58opens into the cylinder bore 55 on the inner side opposite the outerport 57 and is connected to an axial bore 60 opening into the pumphousing chamber 11 on the side of the cylinder block adjacent the webmember 44.

A pumping piston or plunger 62 is fitted within the end of the cylinderbore 55 adjacent web member 44 and has a head portion 63 adjacent theports 57 and 58 when the piston is in the'retracted position. Piston 62has a tubular skirt portion 64 which extends through a suitable openingin the web member 44 toward the wobble plate 37. A compression spring 66is fitted around this tubular skirt portion 64 and abuts at one endagainst the web member 44. The other end of spring 66 abuts against aspring retainer 67 carried onthe outer end of tubular skirt portion 62.In order to reciprocate the piston 62, a piston rod 69 is located withinthe tubular skirt portion 64 and has a ball end portion 70 which restsagainst a socket on the under side of head portion 63. The other end ofpiston rod 69 has another ball portion 71 fitted within a cup-likerecess '73 on the exposed face of the wobble plate 38. Thus, rotation ofthe drive member 25 and the consequent oscillation of the wobble plate38 will 7 cause the pistons 62 to oscillate with a sinusoidal motionwith a positive return to the retracted position being provided by theaction of compression spring 66.

Within the other end of cylinder bore 55 is slidably fitted a reactionpiston '75 having an axial bore 76 extending from end to endtherethrough. The outlet housing 13 is provided with a recess or bore 78in axial alignment with reaction piston '75, and within this recess ismounted a port member 79 having an axial bore 80 in alignment with theaxial bore '76 and the reaction piston. A short compression spring 82 isfitted around the end of reaction piston to abut at one end against. asnap ring 83 secured to the reaction piston and at the other end againsta retainer plate 84 secured to the outlet housing 13 by suitable screwsindicated at 85. Compression spring 82 serves to bias the reactionpiston 75 into sealing engagement against the end of port member 79while permitting a certain amount of transverse movement between them tocompensate for possible misalignment. Within recess 78, a check valveplate 8'7 is fitted over the other end of port member bore to makesealing contact therewith under the bias of compression spring 88. Theother end of compression spring 88 is fitted within a cage 8? held inplace by a plug 90 which closes oil? the outer end of recess 78. Apassage $2 is provided in the outlet housing to conduct fluid from therecess 78 into an outlet chamber 93 centrally located on the outlethousing and having a threaded portion 94 to receive a suitable couplingor pipe fitting for connection to the hydraulic circuit operated by thepump.

When the pump is operating atmaximum output volume, the cylinder blockis in the position shown in FIG. 1 adjacent the web member 44. Thecylinder block is normally maintained in this position by the bias ofanaxially located compression spring 97 which abuts at one end in therecess 8 formed in the end of .cylinder block 50 and at the other end isfitted over a'boss 99 formed on the interior of outlet housing 13.

In order to reduce the effective output volume of the pump, a fluidmotor assembly 100 is provided to shift the cylinder block 50 toward theoutlet housing 13 against the biasing force of the compression spring97. Fluid motor assembly 100 includes a piston member 101 secured in acentrally located aperture 102m the cylinder block 56. Piston member 101is secured against axial movement by flange 103 and snap ring 104. Thepiston member 101 has an end or head portion 106 which is slidablyreceived within an axial bore 108 in cylinder member 167. The cylindermember 107 is mounted within an axial bore 111 in the central bossportion of the web member 144. A shoulder 113 and snap ring 114 serve tosecure the cylinder member 107 against axial movement with respect tothe web member 44 and boss 110.

A floating piston 116 is fitted within the cylinder bore 108 and isprovided with a projection 118 to space the piston 116 away from the endwall 119 of the cylinder member. The space surrounding the projection113 forms a first expansible chamber fluid motor 121. On the other sideof the floating piston 116 there is a longer projection 123, which abutsagainst the end of the piston head 166 to space the latter away from theend wall 119 and thereby define a limiting position to the cylinderblock under the bias of the compression spring 97. The space surroundingthe projection 123 forms a second expansible chamber fluid motor 124which is sealed off from the other chamber 121by means of the floatingpiston 116.

Fluid is admitted to chamber 121 by means of a radial port 127 in thewall of cylinder member 107. Port 127 on the outside connects withlongitudinal groove 126 formed .in the outer periphery of cylindermember 107 in axial alignment with a radial passage 128 in the webmember 44. In like manner, chamber 124 is connected through a radialport 131 through a groove 130 on the outer periphery of cylinder member.107, and groove 130 is in radial registration with a radial passage 132formed in a web member 44 substantially diametrically opposite the otherradial passage 128. It will therefore be seen that by selectivelycontrolling the admission and exhaust of fluid through the radialpassages 128 and 132, the amount of fluid within the chambers 121 and124, respectively, may be controlled to thereby control the axialposition of the cylinder block 50.

The control valve for varying the effective output displacement of thepump by controlling the flow of fluid to and from motor chamber 121 isindicated generally at 150 and is shown in detail in FIGS. 3 and'5.Control valve 158 includes a valve housing 151 secured on a boss 148 onthe external surface of pump housing by suitable cap screws 149. Valvehousing 151 has an axial bore 152 in which is slidably journaled a valvespool 155. The valve spool 155 has a pair of annular grooves 156 and 158which define a land portion 157 between them. At one end, valve spool155 has an outer land 159 sealing off axial bore 152 outward of groove156. At the other end, the valve spool has a guide land 161 outward ofthe other groove 158, and flats 162 are provided on land 161 to allowfluid flow past the land.

A transversely extending control pressure bore 164 is formed in thevalve housing 151 and extends across the axial bore 152 adjacent theland 157. To permit fluid flow between both sides of bore 164, the land157 is provided with an annular groove 165 at its mid portion. Outletpressure is admitted to axial bore 152 adjacent groove 166 by a pressurepassage 167. Pressure passage 167 extends radially to bore 148 where itis connected to a passage 168 formed in the wall of pump housing 10.Further connection is made through a fitting arrangement 171) to connectthe passage 168 to a radial passage 171 formed in the outlet housing 13and opening into the output chamber 93. Thus, passage 167 serves toadmit fluid at full outlet pressure at all times to the groove 156 onvalve spool 155.

A drain passage 173 is providedin valve housing 151 and opens into axialbore 152 adjacent the other groove 158. Drain passage 173 connects withanother drain passage 174 formed in the pump housing wall 10 and openinginto the pump chamber 11. Further connection between the control valve150 and the pump is made by a connecting tube 146 which extends atoneend into a counterbore in the control pressure bore 164 and at the otherend inwardly through the pump housing wall 10 into a counterbore withinthe web member-44 where it 7 connects to the'radial passage 128 leadinginto chamber 121.

At the end of. valve spool 155 having land 159, there is fitted a springabutment 177 Within a chamber 178 formed in the valve housing. Acompression spring 1'79 is mounted within chamber 178 to abut at its oneend against spring abutment 177 and at its other end against a piston180 slidably mounted within bore portion 181 of chamber 178. Chamber 178is connected by a suitable passage (not shown) to drain passage 173 toprevent possible buildup of fluid pressure within chamber 178' as aresult of leakage past the outer land 159.

By virtue of the connectionthrough spring 179, movement of the piston180 along bore 181 provides a variable biasing force on the valve spool155. To provide means for moving the piston 180, a control arrangementis provided as shown in FIG. 5 The valve housing 151 is provided on itsouter periphery with a forked boss 183 which supports a pivot pin 184 onwhich is journaled one end of a lever 186 which extends transverselyacross the opening of bore 181. At its other end, lever 186 is providedwith a suitable connection to a control rod 187 for rotating the leverabout pivot pin 184. Adjacent its mid point, lever 186 is provided witha longitudinal slot 189 in which is located a roller 190 journaled on apivot pin 191 carried in the lever 186. Thus movement of the control rod187 will cause movement of the roller 190 to contact the piston 180 andshift the axial position of piston 180 along bore 181. To limit outwardmovement of the roller 190 and piston 180, lever 186 is provided with aprojecting lug 193 adjacent pivot pin 184. A stop screw 194 isthreadedly engaged in lug 193 and held in place by lock nut 195. Byvirtue of engagement between the end of stop screw 194 and the outersurface 196 of valve housing 151, rotation of the lever 186 is limitedto define an outermost position of piston 180.

At the other end of valve housing 151, land 161 on valve spool projectsinto a counterbore 198 which opens into a larger counterbore 199.Counterbore 199 is closed oil. by a cap 200 held in place by suitablecap screws 201. Cap 200 is provided with an axial extension 202 whichextends into counterbore 198 to make sealing contact therewith. Thechamber within counterbore 198 is thus sealed off from counterbore 199and connected by means of flats 162 on land 161 to the drain passage173. Counterbore 199 is connected through the passage 286 to the controlpressure bore 164 so that at all times it is subjected to the controlpressure within chamber 121. The extension 202 has an axial bore 203 inwhich is slidably journaled a small piston 204. A radial passage 205extends through the walls of extension 282 to connect bore 203 to theconunterbore 199. Thus piston 284 which abuts against the end of valvespool 155 is at all times subjected to the control pressure withinchamber 121, and this control pressure thus acts as a biasing force onvalve spool 155 to oppose the biasing force of compression spring 179.

From the above description it will be seen that the position of thevalve spool 155 depends upon the balance of forces between the controlpressure in chamber 121 acting on piston 204 and the biasing force ofcompression spring 179 as determined by the position of piston 180.Since the fiuid pressure within chamber 121 is directly propor tional tothe force exerted on the cylinder block by the spring 97, the controlpressure within chamber 121 varies with the position of the cylinderblock with an increasing pressure at cylinder block positionscorresponding to decreased pump output displacement. When piston isshifted inward to compress spring 179, the increased biasing force onthe valve spool 155 shifts it toward end cap 200 and fluid at outletpressure in groove 156 is connected to control pressure bore 164 andhence to the chamber 121. This increased pressure causes the piston 116to move and shift the cylinder block 50 to a reduced output displacementposition. Because of the increased force of spring 97 as the cylinderblock is moved in this di-" rection, the control pressure within chamberwill increase until it reachesa level where the biasing force of spring179 is counterbalanced and the valve spool 155 moves back into theneutral position in which the land 157 isolates the control passage bore164 from both of the adjacent grooves 156 and 158. Conversely, adecrease in the biasing force of compression spring 179 will allow thevalve spool to shift in theother direction to connect the controlpressure bore 164 through groove 158 to the drain passages 173 and 174.This allows fluid to flow out of chamber 121 and allows the cylinderblock to move toward a greater output displacement position until thedecreased control pressure in the new position allows the spring 1'79 toshift the valve spool 155 back to the neutral position.

Since the control pressure within chamber 121 required to shift thecylinder block 50 is relatively low compared to the outlet pressure inchamber 93, normal operation of the pump will produce an outlet pressureexceeding the maximum pressure level in chamber 121 and therefore besuificiently high to shift the cylinder block Silaccording to theposition of the piston 126 Since in the balanced position, the outletpressure is not connected to the chamber 121, and the outlet pressureproduces no ubalanced forces on valve spool 155, control valve 15%operates independently of the outlet pressure. Furthermore, since thecontrol pressure is relatively low and the effective area of piston 204relatively small, the counterbalancing force on valve spool 155 isrelatively small and compression spring179 can be made quite light.There fore, only a relatively light force need be applied through thecontrol rod 187 for operation of control valve 1545. Furthermore, sincethe valve spool 155 always returns to the neutral position whentheposition of the cylinder block th is stabilized, and since thecompression spring 179 may have a relatively high spring rate, the rangeof movement of piston 180 needed for the full range of movement'ofcylinder block 5% can be much less than the actual length of movement ofthe cylinder block 50. Thus, not only is the force required foroperating the control valve small, but the distance through which theapplied force moves is also small, thereby providing a very sensitiveand responsive control valve for controlling the output displacement ofthe pump.

As shown in FIG. 1, the pump may also be provided with a separatemanually adjustible stop for positively limiting the maximum outputdisplacement of the pump independently of the operation of control valveThe pump housing ltiis provided with a bore or guide 229 in which aslide 268 is slidably journaled for longitudinal movement parallel tothe axis of the pump. The position of slide 2% is adjusted by a screw21% which is rotated by an external hand wheel 211. A transverselyprojecting pin 212 is secured in slide 2% and extends radially inwardtoward the axis of the pump for engagement against an abutment portion213 formed on cylinder block 59. Thus the pin 212 positively engages thecylinder block 54) through contact with abutment 213 to limit movementof the cylinder block 5i) toward the maximum output displacement underthe action of compression spring 2'7. By

shifting the position of slide and pin 212, this limitirig position canbe varied and the maximum output volume of the pump can be adjusted toany level less than that determined by the full stroke of the pumpingpistons.

The pump is also provided with a pressure compensated valve adapted tolimit the maximum outlet pressure of the pump by shifting the positionof the cylinder block Ell to reduce the output displacement Whenever theoutlet pressure exceeds a predetermined level. The pressure cornpensatedvalve indicated generally at 22% and shown in detail in FIG. 6, isadapted to control the admission of fluid from the pump outlet chamber)3 to the other motor chamber 124 in fluid motor assembly 1%. Thepressure "compensated valve 226 includes a valve housing 221 mounted ona boss 222 formed on the exterior of pump housing 1t opposite thecontrol valve 15d. Valve housing 221 has an axial bore 224 therein'toslidably receive a valve spool 225. The valve spool 225 has a pair ofannular grooves 227 and 228 whichdefine a valving land 229 between them.At the one end, valve spool 225 is providedwith alongitudinal flat 231,and at this end the axial bore 224 is closed oil by means of a suitableplug 232. The other end 234 of valve spool 225 projects into an enlargedbore 235 in valve housing 221 where it receives a spring abutmentassembly 236. A helical compression spring 258 is located within theenlarged bore 235 and abuts at the one end against spring abutment 236on valve spool 225 and at the otherend against an adjustable abutment239 which is threadably secured in the outer end of enlarged bore 235and fixed in place by suitable lock nut 24%.

The valve spool grooves 227 and 228 together with the land 229cooperatewith an arrangment of ports to control the flow of fluid through thevalve. Accordingly, a

control pressure port 243 opens into the axial bore 224' opposite theland 229 and it is substantially the same width as land 22950 that thelatter is able to block off port 243 only when it is in exact alignmentwith the port. An outlet pressure port 244 opens into axial bore 224opposite the one annular groove 22?; and end portion 231, while a drainport 245 opens into axial bore 224 opposite groove 227. A passage 247extends from the control pressure port 243 to the enlarged bore 235 sothe fluid in the latter is always at the control pressure. The controlpressure port 243 is connected by a tube 24-2 which extends to the wallof pump housing 15) and into the web member 44 to connect with-theradial passage 132. A drain passage 251 also extends to the wall of pumphousing it) to connect the drain port 245 to the pump housing chamber11. Pressure is delivered to the outlet pressure port 24 by means of aradial passage 253 which extends through the wall of pump housing it}where it connects with an axial passage 254. In turn, axial passage 25extends axially within pump housing 1% to a connecting angle fitting 255which is also connected through a radial passage 257 in the outlethousing 13 to the outlet chamber 93.

It willtherefore be seen that the axial position of the valve spool 225and hence the valving action of pressure compensated valve 220 willdepend upon the balance of forces acting on the opposite ends 231 and234 of the valve spool. The one end 231 is always exposed to the outletpressure communicated through port 244 and this pressure tends to biasthe valve spool 225 in a direction to bring the groove 22% intoalignment with the control pressure port 243 and thereby allow theoutletpressure from port 24-4 to be communicated through the tube 49 andpassage 132 to the chamber 124 in fluid motor assembly 1.00. Thispressure force is opposed by the combined force of the compressionspring 238 acting against the spring abutment 23d and the controlpressure within enlarged bore 235 acting on the cross-sectional area ofthe valve spool. Since the control'pressure is relatively low, it willbe seen that the compression spring 238 provides most of the forceopposing the outlet pressure acting on the other end of the valve spool;The force of the compression spring 233 may therefore be regulated bythe threaded adjustment of the abutment 239 so as to limit the maximumoutlet pressure of the pump.

When the outlet pressure is below the maximum level determined by theposition of threaded abutment 239, compression spring 238 shifts thevalve spool 225 so that the control pressure port 243 is incommunication with groove 2217 and hence with the drain port 245.Therefore, the motor chamber 124 will be connected with'drain so thatany fluid therein will be exhausted and the piston head 1% will be in anabutting engagement with the projection 123 including piston 116.Increasing outlet pressure at port 244- acts on the end'231 of valvespool 225 tending to shift the latter toward the left as seen in FIG. 6to compress the spring 238. The limiting maximum pressure is determinedwhen the land 22% is shifted intoa position where the control pressureport 244 is connected with the groove 228 to allow the relatively highoutlet pressure to enter the control port 243 and pass in the aforesaidmanner into the motor chamber 124. When this pressure level is reached,the high pressure fluid from the outlet port acts on both the floatingpiston 116 and the piston head 1%. Since the floating piston 116 is freeto move within the bore 168, the high pressure outlet fluid will tend toforce the floating piston toward the end wall 119 and thereby raise thecontrol pressure within chamber 121. This increase in pressure inchamber 121 tends to shift the valve spool of control valve 151 in adirection to permit the fluid within chamber 121 to drain 'into the pumphousing chamber 11 and thereby allow the floating piston 116 to come torest in engagement with end wall 119.

At the same time, the force of the outlet pressure fluid within chamber124 acts on the piston head 106 to shift the cylinder block 50 towardthe outlet housing 13 against the force of spring 97 and thereby reducethe outlet displacement of the pump regardless of the position of thecylinder block 50 as previously determined by the manual control ofvalve 150. Thus the pressure compensated valve 220 always acts tooverride the operation of the manual control valve 150 to positivelyprevent a build up of fluid pressure in the outlet chamber 93 above thelevel determined by the position of the threaded abutment 239. As soonas the outlet pressure drops below this level, the spring 238 willovercome the outlet pressure force acting on the other end'of valvespool 225 to shift the latter into a position where the fluid Withinchamber 124 will be connected through groove 227 to the drain port 245and drain into the pump housing chamber 11 through drain passage 251.Whenever this happens, the pressure Within the other motor chamber 121will drop to the original level and thereby operate the manual valve 150to admit fluid into chamber 121 and thereby allow the cylinder block 50to return under the action of spring 97 to the original position wherethe pressure in chamber 121 balances the biasing force of thecontrolspring 179'. It will therefore be seen that as soon as a high pressurecondition has been overcome by relief in the external circuit of thepump, the output displacement of the pump will rise immediately from thelow position required by the pressure compensated valve 220 to thesetting determined by the control valve 150 and remain at this leveluntil changed by action of either the external control valve 150 or areoccurrence of excessive pressure acting on the pressure compensatedvalve 220.

While the preferred embodiment of the invention has been shown anddescribed in detail, it is understood that this invention can take manyother forms and embodiments, and that such forms and embodiments as mayoccur to those skilled in the art may be resorted to without departingfrom the scope of the invention as defined in the following claims.

What is claimed is:

1. A variable displacement pump having a pump housing and a pumpingmechanism within said housing, said pumping mechanism including amovable member for varying the effective displacement of the pump and afluid motor for shifting said movable member in one direction, springmeans biasing said movable member in the other direction, a controlvalve for controlling the flow of fluid to and from said fluid motor,said control valve including a control valve housing, a bore in saidcontrol valve housing, a valve spool axially slidable in said bore, portmeans cooperable with said valve spool whereby movement of said valvespool in one direction connects said fluid motor to said pump outlet andmovement of said valve spool in the other direction connects said fluidmotor to drain, control means to apply a variable springbias tending toshift said valve spool in one of said directions, and fluid pressuremeans responsive under static conditions solely topressure in said fluidmotor to bias said valve spool in the other of said directions tocounterbalance said spring bias.

2. A variable displacement pump having a pump housing and a pumpingmechanism within said housing, said pumping mechanism including amovable member for varying the effective displacement of the pump and afluid motor for shifting said movable member in one direction, springmeans biasing said movable member in the other direction, a controlvalve for controlling the flowof fluid to and from said fluid motor,said control valve including a control valve housing, a longitudinalbore in said control valve housing, a valve spool axially slidable insaid bore, port means in said control valve housing cooperable with saidvalve spool whereby movement of said valve spool in one directionconnects said fluid motor to said pump outlet and movement of said valvespool in the other direction connects said fluid motor to drain, controlmeans to apply a variable spring bias tending to shift said valve spoolin one of said directions, and piston means operable under staticconditions solely by fluid pressure in said fluid motor to bias saidvalve spool in the other of said directions to counterbalance saidspring bias, said piston means having a cross-sectional area less thanthe cross-sectional area of said valve spool.

3. A variable displacement pump comprising a pump housing having a fluidchamber therein, an outlet on said pump housing and an inlet to saidfluid chamber, a cylinder block slidably mounted within said pumphousing for movement along a longitudinal axis, said cylinder blockhaving a plurality of cylinder bores extending longitudinally therein, apumping piston in one end of each of said cylinder bores, drive means toreciprocate said pumping pistons, a tubular reaction piston in the otherend of each of said cylinder bores, check valve means interconnectingsaid reaction pistons and said outlet, inlet port means on said cylinderblock opening into each of said cylinder bores intermediate the pumpingpiston and the reaction piston, spring means biasing said cylinder blocktoward said pumping pistons, a fluid motor adapted to shift saidcylinder block toward said reaction pistons to oppose said spring means,and a control valve for controlling the flow of fluid to and from saidfluid motor, said control valve including a control valve housing onsaid pump housing, a bore in said control valve housing, a valve spoolaxially slidable in said bore, port means cooperable with said valvespool whereby movement of said valve spool in one directionconnects-said fluid motor to said pump outlet and movement of said valvespool in the other direction connects said fluid motor to said fluidchamber, control means to apply a variable spring bias tending to shiftsaid valve spool in said one direction, and fluid pressure meansresponsive to pressure in said fluid motor to bias said valve spool insaid other direction.

4. A variable displament pump comprising a pump housing having a fluidchamber therein, an outlet on said for movement along a longitudinalaxis, said cylinder block having a plurality of cylinder bores extendinglon gitudinally therein, a pumping piston in one end of each of saidcylinder bores, drive means to reciprocate said pumping pistons, atubular reaction piston in the other end of each of said cylinder bores,check valve means interconnecting said reaction pistons and said outlet,inlet port means on said cylinder block opening into each of saidcylinder bores intermediate the pumping piston and the reaction piston,spring means biasing said cylinder block toward said pumping pistons, afluid motor adapted to shift said cylinder block toward said reactionpistons to oppose said spring means, and a control valve for controllingthe flow of fluid to and from said fluid motor, said control valveincluding a control valve housing secured to said pump housing, a borein said control valve housing, a valve spool axially slidable in saidbore, port means cooperable with valve spool whereby movement of saidvalve spool in one direction connects said fluid motor to said pumpoutlet and movement of said valve spool in the other direction connectssaid fluid motor to said fluid chamber, manual control means to apply avariable spring bias tending to shift said valve spool in said onedirection, and a piston and cylinder motor operable by fluid pressure insaid fluid motor to shift said 'valve spool in said other direction,said piston and cylincross-sec- 1 l fluid motor for shifting saidmovable member, spring means biasing said movable member in oppositionto said fluid motor, a control valve for controlling the flow of fluidto and from said fluid motor, said control valve including a controlvalve housing secured to said pump housing, a first bore in said controlvalve housing, a valve spool axially slidable in said first bore, afirst port opening into said first bore and connected to the pumpoutlet, a second port opening into said first bore and con nected tosaid fluid motor, a third port opening into said bore and connected tosaid fluid chamber, a land on said valve spool adapted to close off saidsecond-port, a first groove on said valve spool adjacent said landopposite said first port, a second groove on said valve spool adjacentsaid land opposite said third port, an enlarged counterbore in saidcontrol valve housing coaxial with said first bore adjacent one end ofsaid valve spool, a first piston slidable in said counterbore, controlspring means within said counterbore abutting at one end against saidfirst piston and at the other end against said one end of said valvespool, manual control means to move said first piston axially withinsaid counterbore, a second bore in said control valve housing having adiameter less than that of said first bore, atsecond piston slidable insaid second bore and engageable with the outer 'end of said valve spool,and passage means in said control valve housing interconnecting saidsecond port and said second bore whereby said second piston biases saidvalve spool against adapted to connect said second-fluid-motorto' saidpump outlet and to drain, said second control valve including a valvespool axially shiftable in one direction to interconnect the secondfluid motor With said pump outlet and shirtable in the other directionto connect said second fluid motor to drain, manual control means forapplying a variable spring bias tending to shift said valve-spool insaid one direction, and fluid pressure means operable by the pressure insaid second fluid motor to shift said valve spool in said otherdirection.

8. A variable displacement pump having a pump hous- 7 ing and a pumpingmechanism withinsaid pump houssaid control spring means with a' forceproportional to the fluid pressure in said fluid motor.

means biasing said cylinder block toward the maximum output displacementposition, a first expansible chamber fluid motor coaxial with saidlongitudinal axis and adapted to shift said cylinder block against thebias of said spring means, a first control valve adapted to connect saidfirst fluid motor to said pump outlet and to drain, said first controlvalve being operable When the pump outlet pressure exceeds apredetermined level to admit fluid pressure into said first fluid motorto reduce the effective output displacement of the pump, a second fluidmotor coaxial with said longitudinal axis and adapted to shift saidcylinder block against the bias of said spring means, a second controlvalve'adapted to connect said second fluid motor to said pump outlet andto drain, said second control valve including a valving member shiftablein one direction to interconnect said second fluid motor with said pumpoutlet and shiftable in the other direction to connect said second fluidmotor to drain, and manual con biasing said cylinder block toward themaximum output displacement position, a first expansible chamber fluidrnotor coaxial with said longitudinal axis and adapted to shift saidcylinder block against the bias of said spring, a first control valveadapted to connect said first fluid motor to said pump outlet and todrain, said first control valve being operable when the pump outletpressure exceeds a predetermined level to admit fluid pressure into saidfirst fluid motor to reduce the eflfective output displacement of thepump, a second fluid motor coaxial with said longitudinal axis andadapted to shift said cylinder block against the bias of said springmeans, a second control valve ing, said pumping mechanism including acylinder block axially slidable along a longitudinal axis to vary theeffective output displacement of said pump, said cylinder block having aplurality of axially extending cylinders arranged equidistantly aboutsaid longitudinal axis, fluid motor means for shifting said cylinderblock in one direction, means biasing said cylinder block in the otherdirection, saidfluid motor means comprising a cylinder coaxial With saidlongitudinal axis, closure means to seal one end of said cylinder, firstpiston means slidably received in the other end of said cylinder wherebyrelative movement of *said first piston means and said cylinder shiftssaid cylinder block relative to said pump housing, a second pistonslidably received in said cylinder inter-mediate said closure means andsaid first piston to define a first motor chamber adjacent said firstpiston means and a second motor chamber adjacent said closure means,first control valve means adapted to control the flow of fluid to andfrom said first motor chamber, and second control valve means adapted tocontrolthe flow of fluid to and from said second motor chamber.

9. A variable displacement pump having a pump housingdefining a fluidchamber therein, an inlet to said fluid chamber, an outlet on said pumphousing, pumping mechanism within said pump housing adapted to pumpfluid from said fluid chamber to said outlet, said purnping mechanismincluding a cylinder block axially slidable along a longitudinal axisfor varying the effective-output, displacement of the pump, fluid motormeans for shifting said cylinder block in one direction, spring meansbiasing said cylinder block in the other direction, said fluid motormeans comprising a cylinder coaxial with said longitudinal axis, closuremeans to seal one end of said cylinder, first piston means slidablyreceived in the other end of said cylinder and operatively engaging saidcylinder block whereby relative movement of said first piston means andsaid cylinder shifts said cylinder block relative to said pump housingto vary the output of the pump, a second piston slidably received insaid cylinder intermediate said closure means and said first pistonmeans to define a first motor chamber adjacent said first piston meansand a second motor chamber adjacent saidclosure means, first control'valve means operable responsive to the pressure in said outlet toselectively connect one of said motor chambers to said outlet and todrain, and second control valve means adapted to selectively connect theother motor chamber to said outlet and to drain.

10. A variable displacement pump comprising a pump housing defining afluid chamber therein, an inlet to said chamber, an outlet on said pumphousing, a cylinder block slidably mounted for axial movement along alongitudian axis within said pump housing, a plurality of axially saidhousing coaxial with said longitudinal axis, closure means to seal oneend of said cylinder, first piston means slidably received in the otherend of said cylinder and operatively connected to said cylinder blockwhereby relative movement between said first piston means and saidcylinder shifts said cylinder block relative to said pump housing, asecond piston slidably received in said cylinder intermediate saidclosure means and said first piston means to define a first motorchamber adjacent said piston means and a second motor chamber adjacentsaid closure means, first control valve means operable responsive tofluid pressure in said outlet-to selectively connect said first motorchamber to said outlet and to said fluid chamber, and second controlvalve means adapted to selectively connect said second motor chamber tosaid outlet and to said fluid chamber.

References Cited by the Examiner UNITED STATES PATENTS Webb 91-433 XTucker et al 10338 X Widmer et a1. 103-473 Welborn et al 251-76 Setka251-76 Norlin l03173 Tuck et a1 103-173 Hyler et al. 91433 X GreatBritain.

15 LAURENCE v. EFNER, Primary Examiner.

JOSEPH H. BRANSON, JR., Examiner.

1. A VARIABLE DISPLACEMENT PUMP HAVING A PUMP HOUSING AND A PUMPINGMECHANISM WITHIN SAID HOUSING, SAID PUMPING MECHANISM INCLUDING AMOVABLE MEMBER FOR VARYING THE EFFECTIVE DISPLACEMENT OF THE PUMP AND AFLUID MOTOR FOR SHIFTIONG SAID MOVABLE MEMBER IN ONE DIRECTION, SPRINGMEANS BIASING SAID MOVABLE MEMBER IN THE OTHER DIRECTION, A CONTROLVALVE FOR CONTROLLING THE FLOW OF FLUID TO AND FROM SAID FLUID MOTOR,SAID CONTROL VALVE INCLUDING A CONTROL VALVE HOUSING, A BORE IN SAIDCONTROL VALVE HOUSING, A VALVE SPOOL AXIALLY SLIDABLE IN SAID BORE, PORTMEANS COOPERABLE WITH SAID VALVE SPOOL WHEREBY MOVEMENT OF SAID VALVESPOOL IN ONE DIRECTION CONNECTS SAID FLUID MOTOR TO SAID PUMP OUTLET ANDMOVEMENT OF SAID VALVE SPOOL IN THE OTHER DIRECTION CONNECTS SAID FLUIDMOTOR TO DRAIN, CONTROL MEANS TO APPLY A VARIABLE SPRING BIAS TENDING TOSHIFT SAID VALVE SPOOL IN ONE OF SAID DIRECTIONS AND FLUID PRESSUREMEANS RESPONSIVE UNDER STATIC CONDITIONS SOLELY TO PRESSURE IN SAIDFLUID MOTOR TO BIAS SAID VALVE SPOOL IN THE OTHER OF SAID DIRECTIONS TOCOUNTERBALANCE SAID SPRING BIAS.